Process and plant for continuous manufacture of latex foam articles

ABSTRACT

Process for continuous manufacture of latex foam rest articles ( 2, 38 ) such as mattresses, cushions and the like comprising a part ( 18 ) able to participate to the manufacture steps and to remain embedded in the article with consequent improvements of final performances. 
     A flexible perforated band, preferably a flat polymeric material net ( 18 ) with longitudinal and cross reinforcement members ( 19 ), is placed over a foam laying surface ( 3 ) provided with protuberances ( 7 ) and in continuous advancement between a foam laying station ( 4 ) and an unlimited length article extraction station ( 5 ). 
     The latex foam passes through net holes ( 20 ) forming an upper portion ( 24 ) and a lower portion ( 23 ) relative to said net. The net continuously opposes contraction forces and weight force exerted from upper portion on lower portion. 
     The unlimited length article is subjected to successive cross cuts originating rest articles wherein a foam embedded net is arranged on ends of recesses originated by the protuberances.

The present invention refers to a process and plant for the continuousmanufacture of latex foam rest articles such as mattresses cushions andthe like, and more in particular the invention refers to a process andplant comprising a part useful both for said article manufacture stepscontrol and to improve the features in the article wherein it remainsembedded.

Latex foam articles are known manufactured using a single mould withinwhich a latex foam mixture is subjected to various process steps.

A single mould generally comprises a hollow lower part and an upper partforming the cover, one or the other or even both provided with recessesformation protuberances.

As it is known, initially a latex and its components containing mixtureare prepared.

Latex is an elastomer polymer dispersion in an aqueous serum.

Herein following the term “components” means all those substances,materials, ingredients and/or fillers whose presence is thought beinguseful to carry out optimally latex foam article manufacture steps withdetermined and desired characteristics.

Generally said “components” include surfactants, thickening agents,gelation agents, stabilizers, process accelerators, vulcanisationagents, fillers, and antioxidants.

The process employs a tank within which various components are added toa synthetic or natural rubber mixture.

The raw components prior to their addition to latex are transformed intoan aqueous dispersion by grinders as to reduce particles sizes.

Herein following among most significant components surface active andgelation agents are recalled.

As it is known surfactants determine the presence around each singlelatex particle of a protective barrier opposing their approach; suchbarrier being formed by electric charges all of the same sign for alllatex particles such that they repel each other avoiding a premature andundesired particle coagulation.

Gelation agents have the task of breaking the abovementioned barriersuch that various latex particles, non longer subjected to repulsionforces may come near or away from one another being subjected tovibrations.

During such alternative motion latex particles touch and bond each othercarrying out latex coagulation step.

Referring back to the mould manufacture process, to the latex and itscomponents mixture in the container a pressurized gas is added and themixture is agitated at high speed until its foaming is obtained.

A determined solution of a gelation agent destined to carry out thegelating step is added to the latex foam.

At this time, for a greater clarification in the present invention fieldof application we recall briefly herein that latex foam rest articlescomprise characteristics and process steps different from other foamarticles, for instance polyurethane foam.

As far as the process steps one should remember that latex articlefoaming is achieved inputting an external agent such as pressurized airin the mixture, while polyurethane mixture foaming is achieved by directcontact among polyoil and isocyanate, that is the same base materialsmaking a polyurethane.

Further latex foam articles have a structure mainly provided with tinyopen and uniformly distributed cells for all material thickness,polyurethane foam articles have mainly closed cells except specificpolyurethanes wherein cells are blown up after specific treatments.

A latex foam article manufacture envisages filling up the mould withmixture comprising latex and components already subjected to foaming.

It is to be noted that after foaming the latex mixture is dimensionallyunstable such that a risk exists of a cell walls collapse.

With the aim of facing such risk the gelating step is carried out.

Gelating may be defined as a homogeneous coagulation wherein part of thefoam aqueous serum remains embedded in the rubber polymer. Chemicallygelating is the transition from the “sol” phase to the “gel” phase.Gelating step avoids latex foam collapse after the laying.

The following vulcanisation step is carried out through a vulcanisationagent to determine the final article desired elasticity degree that isthe elastic deformation, density and uniformity article characteristicsthat will assure comfort conditions for the user in a rest state.

During the vulcanisation step the mould is heated preferably with steam.

At the end of the vulcanisation step the mould upper part is rotated orit is lifted with respect to the hollow lower part to allow for articleextraction.

As already mentioned latex foam mixture is an aqueous dispersion whereina considerable amount of water embeds latex particles. For instance ifthe total amount of the latex foam mixture is 100 part in weight, thedry amount is 60 parts in weight and the water amount is 40 parts inweight.

In the various manufacture steps the water amount is diminishing due tophenomena relative to heat absorption by the latex foam.

In the gelation step, necessary to the latex foam dimensionalstabilization, there occur reactions thereto takes part a temperaturesensitive gelation agent in the sense that gelation time decreases withtemperature increase.

Following gelation latex particles coagulate and free water.

In the vulcanisation step the vulcanisation agent under the temperatureinfluence creates bridges between various latex macro-molecules formingsaid particles.

In practice there are formed chemical bonds destined to restrainmacro-molecules unrestrained among themselves and consequently thevolume reduces itself.

After in the drying step the amount of water is removed by evaporationproviding heat to the latex foam by hot air circulation.

The various cited process steps determine material shrinkage phenomenawith consequent reduction of final desired sizes.

Continuous latex foam rest articles manufacture processes are alsoknown.

Such continuous processes are used and described in the assignee patentsEP-B-0,380,963, U.S. Pat. No. 5,229,138, U.S. Pat. No. 6,086,802,EP-A-1,361,033.

Understandably continuous processes permit to achieve high productivitylevels as compared to single mould processes.

Nevertheless continuous processes as single mould ones bring about thecited material shrinkage phenomena relative to the starting programmedamount.

Such material shrinkage is a few percent but brings about anyway a finalproduct dimensional reduction as compared to the programmed.

In particular the material shrinkage is more evident in continuousprocesses where a latex foam block at the end of a daily manufacturecycle takes usually unlimited defined length values.

To clarify which is the material shrinkage phenomenon one thinks that a4% shrinkage relative to a latex foam block of 1,000 meters would implya shrinkage in the block length direction of 40 meters with consequentless production of 40 mattresses if each of them were assigned a 1 meterwidth.

Unfortunately a latex foam article manufacture is very complex becausefirstly it comprises a stable dispersion formation of rubber particlesin an aqueous medium obtained controlling the chemical-physicalproperties of the interface between the aqueous phase and the latexparticles, then the foam formation obtained supplying the gas necessaryto realize the new dispersed phase and the surface energy necessary toform a gas-liquid interface, then the foamed latex gelation achieveddestabilizing the rubber particles-water interface, with eventualbonding of latex particles and formation of a reticular structure thatstiffens the latex foam.

The conditions in which such steps occur are obtained by specificprocess parameters such as time and temperature and appropriatecomponent dosage, according to rules dictated more by experience than bya perfect knowledge of the phenomena involved.

Therefore trying to leave the normal and tested operational conditionsto obviate to the prior cited material shrinkage phenomena may bringabout a variation even negative of the final article performances.

It has then been thought that it was possible to find a solution to thecited problem using a process element able to act on the latex foamblock on continuous manufacture without altering the operationalparameters nor the foam composition and the steps sequence.

Nevertheless even this potential solution did not appear a workable onebecause the shrinkage phenomena occurred within the latex foam and theprocess element might not be extracted from the foam block withoutimpairing the cellular structure.

It was then felt that a possible solution might be found using at leastan element able to be active both in the process steps to control andanyway to counteract the article shrinkage phenomenon and in the finalarticle to provide it with possibly improved performances.

It forms therefore a first aspect of the invention a process forcontinuous manufacture of an unlimited length latex foam block to bedivided in a plurality of articles by cuts transversely to saidunlimited length, comprising the steps of advancing along apredetermined longitudinal direction a laying surface provided withprotuberances between a first and a second station, of laying in saidfirst station a latex foam mixture on said deposit surface in continuousadvancement, of gelating, of vulcanising, of drying characterized by thesteps of:

a) providing, proximate to said first station, a substantially flatflexible band of unlimited length and provided with a plurality ofthrough openings;

b) placing said flexible band on said laying surface protuberances;

c) advancing continuously said flexible band with said laying surface;

d) introducing said mixture in said band openings;

e) forming a latex foam layer comprising a lower portion and an upperportion respectively below and above said band;

f) pressing with said upper portion weight said band against said layingsurface protuberances;

h) gelating, vulcanising, drying said foam block incorporating saidband;

i) cutting said foam continuous block incorporating said band withconsecutive cross cuts displaced one from the other a predetermineddistance.

Preferably said band is from polymeric material.

In the following with the expression “substantially flat and flexibleband provided with a plurality of through openings”, is meant toindicate both a structure formed from a net comprising a plurality oflongitudinal members cross oriented to each other to form meshes whosearea corresponds to said openings either a flexible laminar structureprovided with regular or irregular shape holes corresponding to saidopenings or anyway a flexible structure tape shaped or the like withopenings through which a latex foam passes.

In the following with the expression “polymeric material” is meant toindicate a material generally adapted to said band construction, ofnatural or synthetic type, comprising longitudinal members, such asmono-filaments or braids or fibres for instance of aramide or in generalplastic fibres distributed in an orderly way or in a loose way withoutpreferential orientation for forming nevertheless among them saidopenings, and/or plates, and/or flexible straps in plastic materialhaving openings distributed in orderly or even unorderly fashion.

By the term substantially flat is meant to indicate a band that mightacquire a configuration little different from the flat one for instanceslightly undulated.

Preferably said band consists of a propylene or polythene orpolypropylene or polyamide plastic polymer.

Typically the band is a net or a plate, in single shape or in overlaidlayers.

Conveniently the process is characterized by laying over said band alatex foam of density comprised between 40 to 270 grams/litre when suchlaying surface rate is comprised between 0.3 to 1.5 meters/minute.

Advantageously the process is characterized by laying over saidprotuberances a band resistant to compression forces acting following atleast a first and a second direction perpendicular to each other in asame plane and following a third direction perpendicular to said plane,said at least first and second direction corresponding to thelongitudinal and the cross direction of said latex foam block incontinuous advancement.

Preferably the process is characterized by depositing a band wherein thereaction to said forces exerted on a foam block matches the dimensionalreductions along said first and second direction up to 5% compressionvalue. Conveniently a foam block sample provided with said band withwidth comprised between 180 cm to 220 cm, length comprised between 60 cmto 220 cm, thickness comprised between 10 cm to 240 cm, has a lift valuecomprised between 3% to 15% more as compared a same sample without band.

It constitutes a second aspect of the invention an unlimited lengthlatex foam block continuous manufacture plant to be subdivided in aplurality of articles by cuts transversely to said unlimited length,said plant being formed by a structural part comprising a laying surfacein continuous advancement along a predetermined direction between afirst latex foam laying station and a second said block extractionstation, a plurality of protuberances cantilevering from that layingsurface to a plane parallel to said laying surface plane, a latex foamgelation device, a vulcanisation device before said second extractionstation, a drying device, that plant being characterized by comprisingan auxiliary part in continuous advancement able to take part to theoperation step and to remain embedded in said article by a determinedlength after said block cutting, said auxiliary part comprising anunlimited length flat band and provided with a plurality of throughopenings, said band being placed continuously on said protuberances andassociated to said protuberances by the latex foam passing through saidopenings.

In a third aspect the invention is relative to a latex foam blockcomprising a plurality of lower recesses extending up to a predeterminedheight “s1”, characterized by chemically incorporating along the planeboarding the recesses ends a polymeric material flexible band providedwith through openings.

Conveniently said band in a plastic material net provided with aplurality of meshes forming said openings.

Preferably the foam block comprises a plurality of openings orderedaccording two directions perpendicular to each other in a same plane,said openings having in a direction a pitch comprised between 1 cm to 4cm, and in the other direction a pitch equal to that of the firstdirection or even different.

The present invention will be now further described with the aid of theaccompanying figures, provided in a non-limiting illustrative way,wherein:

FIG. 1 is a longitudinal partial schematic view of the plant accordingto the invention;

FIG. 2 is a longitudinal partial schematic view of the final part ofFIG. 1 plant;

FIG. 3 is a longitudinal partial schematic view of the plant of FIG. 1during a foam block production;

FIG. 4 is a plan view of an auxiliary part of FIG. 1 plant;

FIG. 5 is a schematic plan view of some forces acting on the auxiliarypart of the plant shown in FIG. 4;

FIG. 6 is a plan view of a second embodiment of FIG. 1 plant auxiliarypart;

FIG. 7 is a perspective partial view of the latex foam block shown byFIG. 1 plant 1;

FIG. 8 is a plan view of a third embodiment of FIG. 1 plant auxiliarypart;

FIG. 9 is a longitudinal view of a further embodiment of the latex foamcontinuous block manufacture plant;

FIG. 10 shows a detail of FIG. 9 plant;

FIG. 11 shows a further detail of FIG. 9 plant;

FIG. 12 is a longitudinal section of a mattress manufactured by FIG. 9plant.

In FIGS. 1-3, 1 is a plant for the continuous manufacture of anunlimited length latex foam 2 to be subdivided in a plurality of restarticles such as for instance mattresses.

Plant 1 comprises structural parts and auxiliary parts.

In the following the expression “plant structural parts” means, asalready known in traditional techniques, means, accessories and devicesnecessary for block manufacture and the expression “plant auxiliaryparts” indicates, according to the present invention, means capable toinfluence advantageously both the block manufacture steps and the finalarticles performances.

Therefore said plant structural parts are absent in the final articlewhile said plant auxiliary parts to achieve the invention aims arepresent both during the plant operation and in the final article.

Now the plant 1 structural parts are described.

Such plant 1 structural parts comprise a latex foam laying surface 3 incontinuous advancement along a predetermined longitudinal direction “F”between first foam laying station 4 and an extraction station 5. Acounter-rotating rollers pair 6 in extraction station 5 carries block 2towards drying device and further possible plant devices and finally toa cutting station for the formation of an plurality of articles.

Laying surface 3 comprises a plurality of protuberances 7 cantileveringfrom the base to form, as it is known, a plurality of lower recesses inthe foam block.

The protuberances ends lie along an imaginary plane at a determinedheight “s1” with respect to laying surface 3.

Plant 1 structural parts comprise gelation means 8 followed byvulcanisation means 9.

Both such means 8, 9 are placed between first and second station 4, 5.Gelation means in their most general embodiment must be able tostabilize the latex foam and to this purpose they use heat sources ableto provide temperatures from 18° to 55° degrees centigrade, and morepreferably from 27° to 49° C., in the environment crossed by the latexfoam block.

Near first station 4 is placed a laying device 10 of a latex foam basemixture destined to form a block 2 base layer and at a short distancefrom first station is placed a foam levelling doctor blade 11.

Said laying device 10 is moved in a cross direction to surface 3advancement direction and coming near or away from such surface 3 inarrows “f” direction by adequate slide guide and drive means notillustrated because of any known type.

Further laying device 10 is connected to a latex mixer.

Said mixer comprises multiple tanks and various equipment, among whichthe control, supply, send and connection ones.

For description shortage said mixer has been exemplified with a singletank 12 provided with appropriate connection piping to a mixture layinghead 13.

Preferably gelation means 8 and vulcanisation means 9 comprise a singletunnel type device partitioned in a first and a second chamber 15, 16.

The tunnel is heated with 100° C. steam.

The plant final part comprises a drying device 14 and a cutting station17 wherein a blade or similar means separate the continuously movedblock portion from the block portion destined to form the singlemattress (FIG. 2).

At the end of the plant structural part description now the plant 1auxiliary parts are described that form the inventive solution of thepresent invention.

Said auxiliary parts consist in a flexible plastic band flat shapedprovided with a plurality of through openings.

Said band, as explained later, is an active part in the manufactureprocess in conjunction with laying surface 3 protuberances 7.

In a description example said band is formed from a plastic net 18comprising (FIG. 4) a plurality of longitudinal members 19 crossoriented one to another to form a plurality of meshes bounding throughopenings 20.

In the description example plastic material net 18, such as high densitypolyethylene or propylene or polyamide or other equivalent materials, isobtained for example in some instances by extrusion and in others byheat-seal.

Said various longitudinal members 19 may be thermoplasticmono-filaments, placed according rows preferably but not necessarilyperpendicular to each other in the same plane.

Such longitudinal members have a diameter comprised from 1 to 7 mm andare restrained solidly between themselves in their reciprocal meetingpoints wherein they form nodes 21.

Net 18 presents meshes preferably square shaped, nevertheless accordingto what will be explained later such meshes might take up a differentgeometrical configuration.

Net 18 comprises said plurality of square shaped meshes whose area isidentified from one side by dimensions comprised from 10 to 40 mm.

Now plant 1 operation is described.

Plant 1 operation for an unlimited length foam block 2 manufactureinitially comprises the step of sending net 18 towards laying surface 3already in continuous advancement in F direction towards extractionstation 5.

Before this step net 18 has been preset on already known appropriateaccumulation and feeding means, for instance of the type comprising aplurality of return pulleys set in such a way as to guide the netaccording to an undulated path formed by multiple loops with a fly-wheelfunction.

In a particular embodiment visible in FIG. 1 said accumulation andfeeding means are schematised with single collection coil 22 on whichcylindrical surface is wound a plurality of net concentric loops.

The various loops are unwound and guided, manually or throughmotorization, towards plant 1.

Conveniently net 1 has bending characteristics to wind itself upaccording concentric loops on the cylindrical surfaces of one or morecoils with diameters comprised from 5 cm to 100 cm.

Net 18 head is connected to some laying surface 3 protuberances 7 top.

Net 18 dragging by laying surface 3 advancement brings the net in firststation 4 zone wherein laying device 10 is activated.

In first station 4 laying head 13 moved in a direction and in the opposeone across to the laying surface 3 advancement direction sends latexfoam downward forcing it to pass through net openings 20.

Now latex foam propagates between laying surface 3 protuberances 7 andover net 18.

It is highlighted that net 18 is now already stably anchored to latexfoam.

The net bounds two foam portions in the following called lower portion23 with a thickness s1 and upper portion 24 with a thickness s2 (FIG.3). Foam block 2 proceeds its path in longitudinal direction “F” and inpassing under doctor blade 11 is leveled acquiring on the outside asubstantially flat shape.

The foam blocks manufactured with the process being described have athickness s1 in lower portion 23 comprised from 9 cm to 15 cm, and athickness s2 in upper portion 24 comprised between 9 to 15 cm.

Then block 2 always associated to laying surface 3 reaches and passesthrough gelation 8 and vulcanisation 9 device receiving the heatnecessary with respect to its dimensional stabilization and its chemicalreticulation.

Foam block 2 along the whole path from laying station 4 to vulcanisationdevice and thereafter to drying device 14 is subjected to contractionforces and thereafter to the weight force exerted by upper portion 24towards lower portion 23.

In the state of the art relative to traditional plants, said forceseffect is not counteracted, therefore the foamed material reduces itselfwith respect to the desired dimensions.

Advantageously net 18 forms that plant 1 auxiliary part able to limit ifnot to completely cancel the cited forces effect.

Net 18 is pressed towards the plurality of protuberances 7.

Due to the effect of upper foam weight 24 all crossing nodes of net 18longitudinal members 19 are blocked, therefore any relative motion amongvarious nodes is prevented.

Referring now to net 18 schematically represented in FIG. 5 plain viewit is highlighted that latex foam possible contractions indicated withopposite arrows in a determined direction and with t letter unloadthemselves upon longitudinal members 19, but due to the fact nodes 21remain in an unchanged position, contraction forces effect “t” might notbe able to do nothing but bend longitudinal member 19.

Nevertheless the conveniently adapted mechanical characteristics for thenet are such as to substantially limit the deformation values,counteracting in such manner the effects otherwise following thecontractions presence.

The previous consideration has been made relative to the horizontalcontraction forces present in one block 2 plane but because variousupper portion 24 planes are bound to one another by the same cellularstructure, one has the effect that all planes contractions transferitself to the plane provided with more resistance and that is thenearest to net 18.

Further the previous considerations referred to horizontal contractionsmay be referred in the same manner to upper portion 24 weight effectswith respect to lower portion 23.

In particular as may be noted in FIG. 3, upper portion 24 weight unloaditself on the various sections of longitudinal member lying on the endsof a protuberances pair 7 proximate to each other; each said portionbehaves like a civil construction beam which uniformly loaded for allits length, unload the weight loaded on it to the extreme abutmentsrealized with high mechanical strength.

The previous description was made relative to a net wherein variouslongitudinal members 19 are cross-oriented to each other and restrainedto nodes 21, nevertheless are within the scope of the invention plasticnets whose various longitudinal members are not rigidly restrained toeach other in the cross points such as illustrated by way of example inFIG. 6 or also for instance when the net takes up a configurationsimilar to a non woven fabric and anyway be provided with openings ableto be crossed by a latex foam. Referring to FIG. 6 net it is to beobserved that longitudinal members 19 meet in the plurality of points 21subjected to compression forces due to foam upper portion 24 weight.

Thus such points 21 stay in an unvaried position to each other allowingnet 18 to abide to its plant auxiliary part previously explainedfunction.

Further a major part of upper portion weight 24 unloads itself on thewide surface distribution of resisting members in the net reducing inthis manner the compression effect on lower portion 23, thereforestabilizing said lower portion density as desired.

Taking back up the plant operation it is to be noted that foam block 2incorporating net 18 advances in predetermined longitudinal direction“F” remaining associated to laying surface 3 until when in the passagethrough 6 rollers pair is detached from said laying surface and pushedcontinuously towards drying device 14 and then towards cutting station17.

In cutting station 17 (FIG. 2) foam block 2 advances underneath anappropriate cutting blade 26 for a section corresponding to a desiredwidth dimension of a single mattress.

After such section measurement, carried out by various optical and/ormechanical devices known by themselves, blade 26 is lowered until itseparates the single mattress for cross cutting (FIG. 7) from foam block2 always in continuous advancement.

It is to be noted that net 18 from the vulcaniser exit to cuttingstation 17 goes on carrying out its plant auxiliary part function andafter cutting, net portion 18 incorporated in single mattress bodycontributes with its characteristics to improving the elastic strengthof the foam whole cellular structure wherein it is embedded.

Up to this point the description has been made relative to a plant 1comprising a laying surface 3 schematically indicated with a straightline.

Such laying surface 3 might take up various embodiments and among theseis mentioned that described in patent EP 0,358,914 herein incorporatedin case a detailed explanation of its operation might be necessary.

In the following it is briefly indicated that laying surface 3 belongsto a motion transmission made up by a plurality of lower plates side byside to each other and cross-anchored to two chains (not shown) arrangedin an annular configuration around two pulleys, one of which a driveone.

Such plates, preferably in aluminium, comprise protuberances 7,preferably hollow, useful both for lower recesses moulding 7′ (FIG. 7)in the base layer and to gelate and vulcanise in a diffused manner thelatex foam mass.

To understand even better the core of the invention is underlined thatplant 1 description has been made referring to a flexible plastic bandwith a net shape, nevertheless said band might take up differentconfigurations.

To that end in FIG. 8 it has been indicated with the same referencenumerals of previous figures a further perforated band, made up fromplastic material and with a configuration corresponding to a flexiblelaminar structure 18 provided with through holes 20.

Said through holes might be of circular shape, non necessarily of equaldiameter, or of square or rectangular shape, or realized according toother geometrical shapes such as for instance hexagonal, octagonal oregg-shaped as both with an equal geometry with each other and with adifferent geometry in one and the same laminar structure.

Advantageously the laminar shape of flexible band 18 allows todistribute over a wide continuous surface the weight force exerted fromupper portion 24 towards lower portion 23, accordingly the pressuresexerted on said lower portion are reduced leaving substantially unvariedthe density with respect to the programmed one at the start.

In all the chosen solutions of the present invention the materialsforming the flexible band must be such as to keep substantiallyunaltered their mechanical strength physical characteristics throughoutall foam block 2 manufacture steps.

In particular the band must be able to withstand, without loosing itsstarting characteristics, at high temperatures both in the vulcanisationstep carried out in the presence of 100° C. steam and in the dying stepcarried out with hot air temperature higher than 100° C.

It is to be underlined at this point as a further characteristic of theinvention the function that might be carried out by openings 20 ofperforated flexible band 18 to control foam density and viscosity.

Relative to the advancement rate of laying surface 3, openings 20 sizeis selected at a start such as to allow a latex foam easy passagethorough band 18.

If after in the manufacture process there might be noticed foamstagnations and/or poor foam filling between protuberances 7, it will bepossible to check if the mistake is to be charged to a variation of foamdensity or viscosity and correct its value, for instance adjusting againchanging during the foaming step the pressurized air to the latex amountratio.

It was found convenient to adopt a density of the foam inputted bydeposition head 13 comprised from 10 to 270 grams/litre when the laying3 surface rate is comprised from 0.3 to 1.5 meters/minute.

In particular it has been found convenient to adopt a perforated band(FIG. 8) with a laminar shape wherein the total voids area isconsiderably greater then full area and preferably a band with a voidsto full ratio from 5 to 2 in combination with foam density andadvancement values just cited.

It is to be underlined that flexible bands 18 may have openings 20distributed unevenly or even according to orderly rows.

Referring to flexible bands 18 with openings 20 distributed evenly inthe following are defined some geometrical characteristics of saidopenings 20 that allow to obtain an even latex foam distribution whenarranged in combination both with protuberances 7, and with the foamdensity and the surface 3 advancement rate having previously citedvalues.

It has been found convenient to adopt flexible bands comprising openings20 oriented according orderly rows in two major directions perpendicularto each other such as represented in FIGS. 4-6.

Preferably said band openings 20 have a minimum dimension, in anydirection, at least greater than 8 mm and extend themselves in a firstlongitudinal dimension with a pitch from 1 cm to 4 cm and in a seconddirection perpendicular to the first one with equal pitch values.

Laying 3 surface protuberances 7 have a circular base with a diameterfrom 2 to 24 mm and a cross dimension of the upper end from 1 to 18 mm.

Further laying 3 surface comprises a number of protuberances 7 from 6 to84 protuberances/square decimetre.

Now in FIG. 9 is described a preferred embodiment of a plant 27 for alatex foam block 2 continuous manufacture comprising both upper recessesand lower recesses.

Plant 27 similar to that described for plant 1 of FIG. 1, is made up bystructural parts and by auxiliary parts.

The plant structural parts correspond substantially to what alreadydescribed in patent EP-A-1,361,033 herein incorporated for any furtherpossible clarification.

In the following are briefly cited the structural parts necessary to theunderstanding of their operation.

Said structural parts comprise a laying surface made up by a pluralityof trucks 28 with protuberances 29 (FIG. 10) moved along an annularcircuit comprising two teethed pulleys one of which a drive one 30, theother a tail one.

The trucks are provided at the lower surface ends with pairs of rollersgeared with the two pulleys grip means and are pushed by drive wheel 30in contact to each other along the active upper branch wherein theyreceive the latex foam through deposition head 13.

The trucks displacement is guided in the upper branch through thesliding of wheels 31 along appropriate guides 32 of a fixed structure.

Lower branch trucks may be in number lower as compared to the upperbranch ones and in this solution they are moved through displacementmeans, such as conveyors 33 and the like, in an way independent from thedrive pulley drives, at a rate higher than the upper branch one.

In the tail branch the trucks rest with side flanges 34 on conveyors 33.

Plant 27 upper part comprises a plurality of plates 35 (FIGS. 9, 11)each of which is provided with a plurality of protuberances 36 adaptedto form upper recesses on the foam block.

Now the auxiliary parts of plant 27 are described.

Said auxiliary parts the same as described in FIG. 1 comprise plasticnet 18 with holes 20 illustrated in FIG. 2.

Net 18 is wound around a collection coil 37 to later pass around coil 22and there from towards the trucks protuberances.

Plant 27 lower part operation is substantially analogous to that of FIG.1, therefore in the following is omitted, for the sake of simplicity,the description relative to plastic net 18 deposition and embeddement inthe foam as well as the function realized by the net as an auxiliarypart of plant 27.

It will be simply said that a latex foam body 38 (FIG. 12) wherein aplastic net 18 is embedded in contact with the upper ends ofprotuberances 29 advances solidly with trucks 28 towards the gelationand vulcanisation device.

The body 38 whole thickness may be from 10 to 30 cm.

Plates 35 are moved along the annular circuit indicated with ABCD.

In the AB portion plates 35 are lowered on the foam body, in the BCportion the plates rest at their ends to the side walls (notillustrated) of the trucks and protuberances 36 are embedded in the foambody.

In the CD portion plates 35 are extracted and lifted one at the timerelative to the foam body and in portion DA the plates go through thereturn branch.

Plant 27 comprises plates 35 lifting and lowering means, realized bypneumatic drives 39 of vertical and horizontal displacement, the latterdisplacement being realized through a member 40 adapted to grip in anopening 41 of each plate 35 (FIG. 11).

Said displacement means act in sections AB, CD.

Plates 35 displacement in upper branch DA is realized through conveyors42.

Advantageously upper plates 35 and relative protuberances 36, preferablyin aluminium, come to the tunnel entry already pre-heated by theprevious passage thorough active section BC.

In plant 27 following sections foam block 38 advances continuouslyassociated to the trucks until the extraction station where it passesthrough rollers 6 detaching itself from the trucks.

The successive steps comprise the block pushing towards the drying andcutting device such as explained referring to FIGS. 1-3.

Foam block 38 after the cut (FIG. 12) comprises upper recesses 43 andlower recesses 44. Recesses 44 upper ends are bounded by net 18.

Plants comprising previously described structural parts and auxiliaryparts allow to reach the predefined aims as highlighted from thefollowing test.

A first and a second latex foam mixtures have been prepared, both of thesame composition and preparation.

The material quantity employed has been determined with the aim tocontinuously manufacture two foam blocks each of 100 metres length, 200cm width, total thickness “S” of 18 cm.

The first mixture has been used to continuously manufacture a firstblock without a flexible perforated band, the other to manufacture asecond block incorporating a flexible perforated band with thecharacteristics described in relation to FIG. 4 example.

The latex foam formulation was as follows:

% parts in weight for 100 Materials parts of dry polymer Natural rubberlatex — Synthetic rubber latex 100 Potassium resinate 1 Antioxidants 0.8Zinc oxide 2 Sulphur 2.5 Accelerators 2 Byphenil-gualidyne 1 Gelationagent: SSF 3

Both mixtures have been used with FIG. 9 plant 27, nevertheless thefirst mixture has been used with plant 27 comprising only the structuralparts and the second mixture with plant 27 comprising also the auxiliaryparts.

The test results have highlighted the dimensional values shown in thefollowing table relative to without band block 1 and with the band block2:

Dimensions Programmed Block 1 Block 2 Length (mt) 100 97 99 Width (cm)200 198 199 Thickness (cm) 18.5 18.4 18.4 % length shrinkage 0 3 1 %width shrinkage 0 1 0.5 % thickness shrinkage 0 0.5 0.5

Advantageously the table results show a significant block 2 materialshrinkage reduction with respect to block 1 referring to the length andwidth desired values.

As far as the thickness values are concerned one may have block 2thickness reductions moderately greater to block 1 thickness reduction,nevertheless it is possible to compensate easily this thicknessreduction adding a small quantity of latex foam material to the startingformulation.

But what has to be highlighted is that thanks to the net presence inblock 2 it is possible to significantly reduce block 2 density withrespect to block 1 keeping the same the two blocks carrying capacity.

If it is now considered an algebraic sum whose factors are the citedmodest latex foam addition for the possible moderate reduction of thethickness of the block 2 with respect to block 1, one can readily seethat the algebraic sum economic value is considerably advantageous forblock 2 as compared to block 1.

In fact, as is obviously understandable, to the cited block 2 densityreduction at equal carrying capacity with block 1 would correspond ahigh material reduction that may be estimated equal to 10% in percentvalue maintaining a carrying capacity value in both blocks substantiallyequal such as for instance 170 Newtons.

Now the advantages derived from the article illustrated in FIG. 12 arehighlighted be it a mattress or a pillow or a part thereof.

The main characteristic of such latex foam is in the combination of aplurality of determined height recesses and of a perforated net placedon the plane where the recesses upper ends are.

The formation of a plurality of recesses obtained, whatever the articlemanufacture process might have been, has guaranteed in the vulcanisationstep through a corresponding protuberances presence an uniform heattransmission through said protuberances with consequent capillary anduniform crosslinking.

The recesses presence in the article then guarantees both an improvedair passage in combination with the channels created by the latex foamcellular structure itself and a uniform elastic deformability withconsequent advantage for the user rest.

The perforated net presence then entails a uniform increased lift of thearticle at equal foam density.

In fact in this article it is noted that the net, blocked during themanufacture process, whatever it may be, over the protuberances due toan upper latex foam portion weight effect, determines the formation of aplurality of latex foam annular configurations concentricallyinterlinked with innumerable hole pairs of the net.

As may be understood such linkage forces the net to lye over therecesses upper ends plane.

Thus if various consecutive cross sections upon the article areconsidered the article carrying capacity is equal in all such varioussections differently from what might happen if the net were placed notaligned relative to the recesses ends, for instance at first aligned andthen with a loop that brings the net to a different height relative tothe recesses upper ends.

1-8. (canceled)
 9. A plant for the continuous manufacture of anunlimited length latex foam block to be subdivided in a plurality ofarticles by cuts transversely to said unlimited length, said plantcomprising: a structural part comprising a laying surface forcontinuously advancing along a predetermined direction between a firstlatex foam laying station and a second block extraction station, aplurality of protuberances cantilevering from said laying surface to aplane parallel to said laying surface, a latex foam gelation device, avulcanisation device before said second extraction station, a dryingdevice, an auxiliary part in continuous advancement capable ofparticipating to the operation steps and remaining embedded in saidarticle for a predetermined length after said block cutting, saidauxiliary part comprising a flexible band substantially flat ofunlimited length and provided with a plurality of through openings, saidband being arranged continuously over said protuberances and associatedto said protuberances by the latex foam passing through said openings.10. Plant according to claim 9, wherein said band is in polymericmaterial.
 11. Plant according to claim 9, wherein said band embedded insaid continuously advancing foam forms means contrasting the contractionforces present on said block.
 12. Plant according to claim 9, whereinsaid band has a laminar structure provided with holes.
 13. Plantaccording to claim 9, wherein said band is made up from a plastic netcomprising a plurality of longitudinal members directed transversely toeach other to form a plurality of meshes.
 14. Plant according to claim9, comprising a coil with a collection seat of said band loops having acylindrical surface with diameter from 5 to 100 cm.
 15. Latex foam blockcomprising a plurality of lower recesses extending up to a predeterminedheight “s1”, incorporating along the plane delimiting the recesses upperends a polymeric material flexible band provided with through openings.16. Latex foam block according to claim 15, wherein the latex foamdensity is from 40 to 270 grams/litre.
 17. Latex foam block according toclaim 15, wherein said band is in plastic material.
 18. Latex foam blockaccording to claim 15, wherein said band comprises a plurality ofthrough openings arranged according to two directions perpendicular toeach other in a same plane, said openings having a pitch from 1 to 4 cm.19. The plant according to claim 9, wherein said block is continuous andthe latex foam of the latex foam block mainly comprising open cells. 20.Latex foam block according to claim 15, wherein said block is continuousand the latex foam of the latex foam block mainly comprising open cells.21. A plant for the continuous manufacture of an unlimited length latexfoam block to be subdivided in a plurality of mattresses by cutstransversely to said unlimited length, comprising: means for advancingalong a predetermined longitudinal direction a laying surface providedwith protuberances, having tapered ends to form recesses in saidmattresses, said laying surface advancing between a first and a secondstation, means for laying in said first station a latex foam mixture onsaid laying surface in continuous advancement, and further comprising:a) means for providing proximate to said first station a substantiallyflat flexible band of unlimited length and provided with a plurality ofthrough openings; b) means for laying said flexible band on said layingsurface protuberances; c) means for advancing continuously said flexibleband with that laying surface; d) means for introducing said mixture insaid band openings, downwardly passing a portion of the mixture throughthe openings; e) means for forming from the mixture a continuous latexfoam layer comprising a lower portion and an upper portion respectivelybelow and above said band, the latex foam mainly comprising open cells;f) means for pressing with said upper portion weight said band againstsaid laying surface protuberances; g) means for gelating, vulcanising,drying said foam layer incorporating said band to form said foam blockof continuous latex foam incorporating said band; h) means for cuttingsaid foam block of continuous latex foam incorporating said band withconsecutive cross cuts at a predetermined distance from each other.